The performance of a recently introduced hybrid of density functional theory and Hartree-Fock theory, the B-LYP/HF procedure, has been examined with a variety of basis sets. We have found that even the relatively small 6-31G* basis set yields atomization energies, ionization potentials and proton affinities whose mean absolute error, compared with a large body of accurate experimental data, is ...

Interaction of meso — tetrakis (p-sulphonato phenyl) porphyrin (hereafter abbreviated to TSPP)with Na+ has been examined using HF level of theory with 6-31G* basis set. Counterpoise (CP)correction has been used to show the extent of the basis set superposition error (BSSE) on thepotential energy curves. The numbers of Na+ have a significant effect on the calculated potentialenergy curve (includ...

A reação da hidroxilamina com acetato de fenila foi investigada teoricamente para se obter uma melhor compreensão do efeito alfa nas reações de nucleófilos neutros. Os cálculos foram feitos em nível B3LYP/6-311+G(2df,2p)//HF/6-31G(d) incluindo o solvente (água) em nível PCM/HF/6-31G(d). Os resultados mostram que um ataque direto da hidroxilamina leva a uma barreira de energia livre de ativação ...

Conformational analyses on 2-substituted (methoxy, vinyloxy, and acetoxy) methylenecyclohexanes have been performed computationally with HF, B3LYP, PBE0, and MP2 and the 6-31G(d) basis set. The global minimum for the methoxy substituent is an axial conformer. For the vinyloxy substituent, except with PBE0, an axial conformer is determined as the global minimum. The acetoxy substituent prefers t...

: In this work, different levels of theory containing HF, B3LYP, and MP2 with different basis sets such as 6-31G, 6-31G*, 6-311G, 6-311+G, 6-31+G*, 6-31+G are used to predict relative acidity constants of some aniline derivatives. Three different kinds of radii containing UAHF, Bondi, and Pauling are used to study how cavity forms change acidity constants. In all cases, DPCM model is used to si...

Several approximate correlation methods have been assessed for bond breaking reactions in BH, HF, and CH4 by comparison to the full configuration interaction limit. Second-order Møller–Plesset perturbation theory, coupled-cluster singles and doubles ~CCSD!, coupled-cluster with perturbative triples @CCSD~T!#, and the hybrid density-functional method Becke three parameter Lee–Yang– Parr have bee...

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds consisting of more than twobenzene rings fused in a linear, angular, or clustered arrangement and do not contain hetero atomsor carry subsistent. PAHs originate from various sources. They are primarily formed byincomplete combustion of carbon-containing fuels such as wood, coal, diesel, fat, or tobacco. Thepresent study reports an...

in this paper, the hydrogen bonding (hb) effects on the nmr chemical shifts of selected atoms in serineand serine-nh2o complexes (from one to ten water molecules) have been investigated with quantummechanical calculations of the 15n and 13c tensors. interaction with water molecules causes importantchanges in geometry and electronic structure of serine.for the compound studied, the most importan...

The geometries of IO, HCIO, ICH2O, CH3IO, CH3OI, CH2IOH, and ICH2OH have been obtained at the HF and MP2(FU)/6-31G(d) levels of ab initio theory, and the HF/6-31G(d) frequencies are compared with experimental assignments where these are available. The Gaussian-2 method was used to provide thermochemical data for use in atmospheric and combustion modeling. Transition states that connect these sp...

In this paper, the hydrogen bonding (HB) effects on the NMR chemical shifts of selected atoms in serineand serine-nH2O complexes (from one to ten water molecules) have been investigated with quantummechanical calculations of the 15N and 13C tensors. Interaction with water molecules causes importantchanges in geometry and electronic structure of serine.For the compound studied, the most importan...